The invention relates to micromechanical optical elements having a reflective surface, which can be deflected in a manner known per se by means of electrostatic or electromagnetic forces, such that incident electromagnetic radiation can be reflected as a function of the respective deflection of the element. The elements according to the invention can advantageously be used in deflection units for laser beams or light beams, bar-code readers, projection displays, retina scanning displays, readers for patterns and images, test equipment, laser printers or direct exposure devices.
Micromirrors such as these are in this case deflected both translationally and rotationally and are then referred to as “pumping or tilting mirrors”. The deflection is in this case carried out at a very high frequency, so that corresponding accelerations occur. Since the deflected elements are normally in the form of plates with a different circumferential geometry, their moment of inertia and the limited strength and stiffness lead to dynamic deformation, which in turn leads to deformation of the reflective surface. With the conventional design of the elements to be deflected, however, even deformation in the nanometer range leads to an undesirable influence on the reflection behaviour.
This negative influence increases as the respective oscillation frequency rises. This can admittedly be counteracted by increasing the strength and stiffness of an element which can be deflected. However, increase in the mass results here, hence the need to increase at least the forces which are required for deflection.
In this case, FIG. 1 illustrates a conventional solution in which an element in the form of a plate is held by two torsion springs arranged mutually opposite, and the element can be pivoted backwards and forwards about the rotation axis on which the torsion springs are arranged. The lower illustration shows, schematically, the dynamic deformation of the element at a point at which the pivoting movement is reversed. The reflective surface is in this case partially convex and concave, so that incident light is reflected differently, depending on the deformation.
However, the dynamic deformation can be reduced only slightly as well by a solution as shown in FIG. 2. This corresponds essentially to the scanner mirrors described in US 2005/0045727 A1. In this case a torsion bar spring is intended to be attached to the mirror at a plurality of points, in which case a solution as shown in FIG. 2 with only two attachment points is used for this specific situation. In addition, however, further spring elements are intended to be formed on the torsion bar along its longitudinal axis, and are intended to be arranged there. This involves a considerable amount of manufacturing effort, since these spring elements must be designed to be very small. It is thus likewise impossible to specifically compensate for forces and torques which have locally different effects because of the moment of inertia, in particular the restoring forces and torques which are initiated by the torsion spring.